The Seeds Beneath the Steps
Sources and reuse terms, checked 2026-09-22

This page ships narrow numeric extracts, one transcribed set of sample labels and one
published calibration curve. It ships no article, figure, photograph or track model.
Every source below is cited on the page field by field.

1. USGS data releases (numeric extracts)
   Bennett and colleagues (2021), Data release for Evidence of humans in North America
   during the Last Glacial Maximum, https://doi.org/10.5066/P9ABZEM9
   Pigati and colleagues (2023), Data release for Independent age estimates resolve the
   controversy of ancient human footprints at White Sands, https://doi.org/10.5066/P9E36U4B
   Shipped: data/seeds.json, data/pollen.json, data/osl.json, data/context.json and
   data/field-map.json, positional extracts of the fields the page needs.
   Both release metadata records state:
     "Although this information product, for the most part, is in the public domain,
     it also contains copyrighted materials as noted in the text. Permission to
     reproduce copyrighted items for other than personal use must be secured from
     the copyright owner."
   Access constraints: NONE. No third-party credit or restriction appears inside the
   numeric files used. This is not read as an unconditional licence for everything in
   either release.
   https://www1.usgs.gov/pir/api/identifiers/USGS:6036950cd34eb12031174c77
   https://www1.usgs.gov/pir/api/identifiers/USGS:647782fed34e3ac335becbb0

2. Sample-number labels (data/layers.json)
   Pigati and colleagues (2023), Science 382(6666), 73-75,
   https://doi.org/10.1126/science.adh5007 . The fourteen short labels printed beside the
   calibrated ages in Figure 2A (for example "21.13±0.25 ka (1a)"), transcribed from the
   article's text layer as factual identifiers. The figure itself is not reproduced.
   The article footer reads: "Copyright © 2023 the authors, some rights reserved;
   exclusive licensee American Association for the Advancement of Science. No claim to
   original US government works."
   Reuse page: https://www.science.org/about/science-licenses-journal-article-reuse
   (it returned HTTP 403 to an automated request on 2026-09-22; no licence is inferred
   from that failed retrieval).

3. IntCal20 (data/intcal20.14c)
   The unmodified curve file from https://intcal.org/curves/intcal20.14c , with its own
   header naming all 42 authors. Paula J. Reimer and colleagues (2020), The IntCal20
   Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP), Radiocarbon
   62(4), 725-757, https://doi.org/10.1017/RDC.2020.41 . The article's first page grants
   Creative Commons Attribution 4.0, https://creativecommons.org/licenses/by/4.0/
   (verified at https://epic.awi.de/id/eprint/53055/1/reimer2020r.pdf). No contrary
   notice appears in the curve file. The article licence and the curve file are distinct
   pieces of evidence; both are attributed here.

4. Articles quoted, linked, not redistributed
   Bennett and colleagues (2021), Science 373(6562), 1528-1531,
   https://doi.org/10.1126/science.abg7586 . The repository page for the accepted
   manuscript quoted on the page, https://eprints.bournemouth.ac.uk/36202/ , states (on
   that page, not inside the PDF): "This is the author’s version of
   the work. It is posted here by permission of the AAAS for personal use, not for
   redistribution." Only short attributed quotations are used.
   Pigati and colleagues (2023), as above: short attributed quotations only.
   Holliday and colleagues (2025), Science Advances 11(25), eadv4951,
   https://doi.org/10.1126/sciadv.adv4951 , CC BY-NC 4.0
   (https://creativecommons.org/licenses/by-nc/4.0/): two short attributed quotations
   and a factual summary; no figure or supplement.
   Madsen and colleagues (2022), https://doi.org/10.1126/science.abm4678 ; Pigati and
   colleagues (2022), https://doi.org/10.1126/science.abm6987 ; Oviatt and colleagues
   (2022), https://doi.org/10.1017/qua.2022.38 ; Rachal, Dello-Russo and Cuba (2024),
   https://doi.org/10.1017/qua.2023.74 ; Rhode and colleagues (2024),
   https://doi.org/10.1080/20555563.2024.2345979 ; Pigati and colleagues (2024),
   https://doi.org/10.1080/20555563.2024.2376298 ; Rachal and Dello-Russo (2025),
   https://doi.org/10.1016/j.jas.2025.106232 ; Springer and colleagues (2026), USGS
   Fact Sheet 2025-3046, https://doi.org/10.3133/fs20253046 . Short attributed
   quotations from abstracts or public records only, or citation alone.

5. Shared site components
   /fonts/fonts.css supplies the site's self-hosted Fraunces and Martian Mono (SIL Open
   Font License). No font file is copied into this stratum.

Everything computed on the page (calibrations, ranges, gaps, sweeps, tests) is this
page's own calculation from the files above.